Soil erosion risk assessment is an essential foundation for the planning and implementation of soil and water conservation projects. The commonality among existing studies is that they considered different indicators (e.g., rainfall and slope) in order to determine the soil erosion risk; however, the majority of studies in China neglect one important indicator, namely the slope aspect. It is widely accepted that the vegetation and distribution of rainfall differs according to the different slope aspects (such as sunny slope and shady slope) and these attributes will accordingly influence the soil erosion. Thus, existing studies neglecting this indicator cannot reflect the soil erosion well. To address this problem, a flexible soil erosion risk assessment method that supports decision makers in identifying priority areas in soil and water conservation planning was developed in the present study. Firstly, in order to verify the impact of the slope aspect on soil erosion, field investigations were conducted, and its impact on the characteristics of the community in the study area was analyzed. Secondly, six assessment indicators were selected, including slope gradient, precipitation, NDVI, land use, soil texture and slope aspect. Next, a developed multi-criteria decision analysis (MCDA) method based on the Choquet integral was adopted to assess the soil erosion risk. The MCDA method, combining objective data with subjective assessment based on Choquet integral, could solve the weight problem encountered when using the quantitative method. The parameters required can be modified according to the soil erosion types, assessment scales, and data availability. The synergistic and inhibitory effects among the soil erosion parameters were also considered in the assessment. Finally, the soil erosion risk results in the Xinshui River watershed revealed that more attention should be paid to the slope of farmland and grassland during the planning and management of soil and water conservation projects. The methodology used in the current study can support decision makers in planning and implementing soil and water conservation measures in regions with different erosion types.

Hydrologic (water temperature) and hydrodynamic (water depth, flow velocity, and Froude number) factors affect fish spawning activities, and spawning grounds provide suitable hydrologic and hydrodynamic conditions for fish spawning to occur. However, locating fish spawning grounds is encumbered by uncertainty, particularly for pelagic spawners. This may be because such fish species have unique hydrologic and hydrodynamic requirements during their spawning periods, resulting in the wide-ranging approaches used to locate their spawning grounds. Accordingly, this study was designed to accurately locate fish spawning grounds through means of spatial suitability evaluation. For this experiment, the four major “Asian carp” target species were selected in the Dongta spawning reach, a tributary of the Pearl River. First, we investigated the historical information on the location of the spawning reaches. An acoustic doppler current profiler (ADCP) was used to measure topographic and hydrodynamic data of the spawning reaches during the spawning period. Then, based on the spatial clustering method, cluster analysis on spatial attributes (water depth, flow velocity, water temperature, and Froude number) was conducted on potential spawning grounds. The cluster analysis method uses k-means clustering; a method often employed to classify large amounts of data. Finally, we analyzed and evaluated the spatial suitability of spawning reaches by combining fish spawning suitability curves to obtain spatial preferences associated with fish spawning activities. Proportionally, results revealed a high suitability (>0.4) area (60.86%). Moreover, spawning suitability in curved river sections and deep pools in straight river sections were significantly higher than bifurcated sections. Furthermore, areas near the riverbanks were more suitable than mid-course sections of the river. Finally, the locations of six potential Asian carp spawning grounds were determined according to their spatial suitability. This study provides technical support to accurately locate spawning grounds for the fish that produce drifting eggs.

Analysis of the spatial variations in river networks and the related influencing factors is crucial for the management and protection of basins. To gain insight into the spatial variations and influencing factors of river networks between large basins, in this study, three river basins from north to south in China (Songhua River Basin, Yellow River Basin and Pearl River Basin) were selected for investigation. First, based on a digital elevation model, different river networks with six drainage accumulation thresholds of three basins were extracted using ArcGIS. The optimal networks were determined through fitting the relationship between the accumulation threshold and related drainage density. Then, we used two indicators, drainage density and water surface ratio, to characterize the spatial variations of three basins. Finally, Pearson’s correlation coefficients were calculated between those two indicators and natural/human influencing factors. The results showed that drainage density and water surface ratio decreased from north to south in China and were negatively correlated with natural/human influencing factors. Drainage density was more influenced by natural factors than by human factors, while the opposite was true for water surface ratio. These findings may provide some basis for the management and protection of the river network.

Water-related ecosystem services (WES) underpin water security but are increasingly threatened by concurrent climate change and land-use change. Yet reliable, generalizable attribution evidence remains limited, because most studies are single-basin and do not explicitly separate climatic and anthropogenic drivers. Here, we implement a scenario-based attribution framework that uses controlled scenario contrasts (climate-only, land-use-only, and coupled scenarios) to quantify and compare the relative contributions of climate and land-use change to two key WES (i.e., water yield and water purification services), and to project WES trajectories for 2020-2100. Using the InVEST Annual Water Yield and Nutrient Delivery Ratio modules, we estimate annual water yield and total nitrogen (TN) export across 17 representative watersheds in China spanning diverse hydroclimatic and landscape settings, and assess WES responses across scenario types. Results show a clear contrast in dominant drivers: climate change affects water yield more than water purification, whereas land-use change affects water purification more than water yield. Climate change contributed >90% to water yields in 15 out of the 17 watersheds; it was 79.4% in the Hei River and only 11.2% in the Yarkant River. For TN export, climate change had a larger influence than land-use change in eight watersheds, exceeding 95% in the Min and Mintuo rivers. For TN export (water purification), climate change had a larger contribution than land-use change in 8 of the 17 watersheds ( >95% in the Min and Mintuo rivers), whereas land-use change dominated in the remaining 9 watersheds ( >95% in the Dongting Lake and Hei River basins). These cross-watershed attribution results identify where climate adaptation versus land-use management is likely to be most effective for sustaining water yield and water quality under future change. The aim of this study is to provide cross-basin attribution evidence that helps target climate adaptation and land-use management to sustain water yield and water quality under future change.

The construction of reservoirs has undeniably provided numerous conveniences and benefits to human societies. However, it has also markedly altered downstream flow regimes, leading to essential fish habitat loss that directly undermines the ecosystem services provided by fish populations, thereby jeopardizing the long-term sustainability of fishery resources. Existing assessments of spawning suitability largely concentrate on static characteristics of available spawning grounds, while the dynamics of habitat suitability migration and contraction in response to changing environmental flows remain poorly understood. To address this gap, we classified hydrological years into wet, flat, and dry categories to reflect the varying environmental flow requirements during the fish-spawning period. Using the Mike21 hydraulic model together with a spatial suitability analysis for spawning habitats, we quantified spawning ground suitability from both temporal and spatial perspectives. Taking the four major Chinese carps (FMCC) and the Dongta spawning ground in the Pearl River as a case study, our findings reveal that the proportion of highly suitable habitats closely tracks the environmental-flow trajectories. Throughout the FMCC spawning period, the spatial pattern of high suitability zones undergoes a marked migration in response to flow variations across wet, flat, and dry years, consistently shifting upstream. Specifically, as discharge rises from low-flow to high-flow events, the most suitable areas move from downstream deep-pool sections toward upstream shallow riffle zones, which is crucial for the sustainable development of fishery resources.